1. Field of the Invention
The present invention relates to a method for producing hydrogen aimed at storage and transportation having a form which is suitable for storage and transportation, in particular, a method for producing hydrogen aimed at storage and transportation with a hydrogenated aromatic compound (organic chemical hydride) produced efficiently at low cost in the organic chemical hydride method, the hydrogenated aromatic compound serving as a hydrogen carrier suitable for bulk storage of hydrogen and/or long distance transportation of hydrogen.
2. Description of the Related Art
In recent years, emission control of carbon dioxide, which is a greenhouse gas, has been gaining momentum. As a result, progress has been made in developing and practically applying hydrogen energy application technologies, which are used for stationary fuel cells, hydrogen vehicles, fuel cell vehicles, and the like. Development has been made intensively for hydrogen storage and transportation technologies to supply hydrogen as a fuel for the stationary fuel cells, hydrogen vehicles, fuel cell vehicles, and the like. Further, as infrastructure for supplying hydrogen to hydrogen vehicles and fuel cell vehicles, the development of a hydrogen station has reached its demonstration stage.
In addition, the hydrogen station includes an on-site type of hydrogen station in which hydrogen is internally produced at station area and an off-site type to which hydrogen produced outside is transported. The former, the on-site hydrogen station, involves a problem in that a large amount of carbon monoxide (CO) is produced as a by-product in the hydrogen production and a considerable amount of carbon dioxide (CO2) is inevitably discharged eventually. Thus, the off-site hydrogen station has been main stream at present.
For the off-site hydrogen station, it is necessary to transport hydrogen produced outside to the hydrogen station. There are known a method for storing and/or transporting hydrogen as compressed hydrogen or liquid hydrogen {for example, see PTL (Patent Literature) No. 1 (JP 4279546 B)} and the so-called organic chemical hydride method, the method involving hydrogenating an aromatic compound such as toluene with hydrogen to be stored, thereby converting the compound into a hydrogenated aromatic compound such as methylcyclohexane (MCH), and then storing and/or transporting the hydrogenated aromatic compound as a chemical in the liquid state at the room temperature under ambient pressure. In particular, the latter, the organic chemical hydride method, is attracting attention because the method does not include a potential risk attributed to ultrahigh pressure or extremely low temperature unlike the former.
For example, “Hydrogen Energy State-of-the-Art Technology” (supervised by Tokio Ohta), NTS Inc. (1995) introduces that the organic chemical hydride method was discussed as an MCH method capable of transporting hydrogen as methylcyclohexane obtained by hydrogenating toluene in the Euro-Quebec Project for producing hydrogen by utilizing electricity generated by abundant hydraulic power in Canada and transporting the hydrogen to Europe across the Atlantic Ocean.
Further, PTL No. 2 (JP 2002-134,141A) proposes a hydrogen storage and supply system for storing or supplying hydrogen by utilizing a hydrogenation reaction to a liquid organic hydrogen storage carrier and a dehydrogenation reaction of a liquid organic hydrogen supply carrier by a metal-supported catalyst, the hydrogen storage and supply system including a hydrogen storage carrier storing part for storing a liquid organic hydrogen storage carrier such as toluene, a hydrogen supply carrier storing part for storing a liquid organic hydrogen supply carrier (hydrogenated aromatic compound) such as methylcyclohexane, a reaction vessel having a metal-supported catalyst for conducting a hydrogenation reaction to the liquid organic hydrogen storage carrier and a dehydrogenation reaction of the liquid organic hydrogen supply carrier, supply means for supplying the liquid organic hydrogen storage carrier or the liquid organic hydrogen supply carrier from the above-mentioned hydrogen storage carrier storing part or the above-mentioned hydrogen supply carrier storing part to the above-mentioned reaction vessel as required, and a hydrogen separator for separating hydrogen generated in the above-mentioned reaction vessel.
Moreover, PTL No. 3 (JP 2007-269,522 A) proposes a storage-transport system of hydrogen by an organic chemical hydride method, including a hydrogen storage system for storing hydrogen as a hydrogenated aromatic compound, a hydrogen supply system for producing hydrogen and an aromatic compound by a dehydrogenation reaction, means for transporting the hydrogenated aromatic compound from the hydrogen storage system to the hydrogen supply system, and recovered aromatic compound transporting means for transporting the aromatic compound from the hydrogen supply system to the hydrogen storage system, the storage-transport system being internally equipped with a reaction inhibitor removal apparatus for removing reaction inhibitors which are poisoning substances to a dehydrogenation catalyst and/or a hydrogenation catalyst, having high storage efficiency of hydrogen, and being capable of easily achieving storage and transportation of hydrogen energy by an organic chemical hydride method (OCH method) with the very simple process.
By the way, many hydrogen supply sources including a water electrolysis process, a gasification process of coal and coke, and by-product hydrogen in refineries are considered. However, at present, the main stream of the hydrogen production is provided from a petroleum refining plant in order to supply a large amount of hydrogen necessary for hydrogenation decomposition for petroleum refining and hydrogenation desulfurization of heavy oil. In the process for hydrogen production, reforming reactions such as a steam reforming reaction, an automatic oxidation reforming reaction, and a partial oxidation reforming reaction are employed by using a naphtha or a natural gas as a feed stock.
In addition, when hydrogen is produced by those reforming reactions, a synthesis gas produced by the reforming reactions includes a large amount of carbon monoxide. Thus, the synthesis gas is purified by causing the carbon monoxide (CO) to react with water vapor (H2O), thereby converting them to carbon dioxide (CO2) and hydrogen (H2) (shift reaction), subsequently subjecting a hydrogen-rich synthesis gas obtained after the shift reaction to acid gas removal treatment, thereby reducing the content of carbon dioxide to about 0.1 to 0.5 vol %, then converting a small amount of remaining carbon monoxide to methane (CH4) in the presence of a hydrogenation catalyst, and carrying out cooling treatment if necessary, to thereby remove by-product methane. Alternatively, in recent years, there have been many cases in which hydrogen purification is carried out by removing an acid gas, carbon monoxide, and methane from a gas after the shift reaction with a pressure swing adsorption (PSA) apparatus, and the resultant hydrogen is commercialized as high-purity hydrogen (99 vol % or more).
Further, Petrochemistry Process, NPTL (Non-Patent Literature) No. 1 {the Japan Petroleum Institute (ed.), pp. 57-67 (1998)} introduces that reforming reaction processes include, in addition to a steam reforming process, a partial oxidation process in which reaction heat is supplied by firing part of hydrocarbon as a material with oxygen and an autothermal reforming process in which reaction is performed in one reaction vessel by combining partial oxidation and steam reforming, and those processes are able to meet a demand for a larger apparatus and to meet a demand for environmental protection, compared with the conventional steam reforming processes. It is further described that progress has also been made in developing a process in which an expensive air separation unit is not used and air is used instead of pure oxygen, however, when nitrogen is separated from a gas of ter a reaction, an accompanying synthesis gas needs to be treated.
On the other hand, Process Handbook, NPTL No. 2 {the Japan Petroleum Institute (ed.), p. 141 (1986)} introduces hydrogenation processes of aromatic compounds which can be used in the organic chemical hydride method. In the process, hydrogenation reaction is carried out in the presence of a hydrogenation catalyst to convert an aromatic compound such as toluene to a hydrogenated aromatic compound such as methylcyclohexane, the amount of heat generation derived from the hydrogenation reaction is large, and hence various methods for removing heat are worked out. One of the methods involves diluting preliminarily hydrogen with an inert gas such as a nitrogen so that a hydrogen concentration is limited to be about 70 vol % or less and then subjecting the resultant mixed gas into the reaction. Thus, it is considered that efficient heat removal allows to carry out reaction at relatively low temperatures at which by-products are produced less. However, a large amount of nitrogen is necessary for the hydrogenation process at a large scale, and when excessive nitrogen is not available, an apparatus for producing nitrogen is required to be provided next to a hydrogenation reaction apparatus.